Polyarylene sulfides and aromatic polyesters are high-performance polymers that may withstand high thermal, chemical, and mechanical stresses and are beneficially utilized in a wide variety of applications.
Each of these polymers can provide advantages to a product composition. For example, polyarylene sulfides have excellent flame resistance, chemical resistance, and high weidline strength. Aromatic polyesters, also referred to as liquid crystal polymers, have good flowability and processibility and can exhibit anisotropic mechanical properties.
In view of the above, those skilled in the art have attempted to combine polyarylene sulfides with liquid crystal polymers in polymer alloys. Unfortunately, liquid crystal polymers are not entirely compatible with polyarylene sulfides. For instance, thermal degradation of the polymers can occur when the polymers are heated together during melt processing, for instance during molding of a composition including the alloy. This thermal instability can produce deposits on the mold surface. Moreover, deposits accumulated on the mold surface can stick to the surface of a molded part. This can cause serious problems including formation of defective parts, particularly when considering parts that are sensitive to contamination, such as connectors for electronic applications. Deposition problems can also cause significant loss in productivity, as deposition can require a continuous molding process to be stopped to clean the mold. In addition to problems associated with deposition due to immiscibility, products incorporating a polyarylene sulfide/liquid crystal polymer alloy have often not obtained desired surface appearance, and particularly desired levels of surface glossiness.
Compatibilizers have been developed to be included in a polyarylene sulfide/liquid crystal polymer alloy and improve stability of the alloy. While use of compatibilizers has improved the alloys, compatibilizers to date have been formed in a separate process and then added with other additives during formation of a composition that includes the polyarylene sulfide/liquid crystal polymer alloy. Separate formation steps for preparation and addition of a compatibilizer can add significant costs to a composite formation process.
Other problems exist with polyarylene sulfide/liquid crystal polymer alloys. For instance, polyarylene sulfides are generally formed via polymerization of p-dichlorobenzene with an alkali metal sulfide or an alkali metal hydrosulfide, forming polymers that include chlorine at the terminal groups. With low halogen-content polymeric materials becoming increasingly desired due to environmental concerns, attempts have been made to produce low chlorine content polyarylene sulfides. In general, this has involved utilizing higher molecular weight polyarylene sulfides in the compositions, as higher molecular weight polyarylene sulfides will include fewer terminal groups and hence have lower chlorine content.
Unfortunately, high molecular weight polyarylene sulfides have high melt viscosity, and this presents processibility issues that may complicate processing techniques, even when the polyarylene sulfide is combined with a liquid crystal polymer that can exhibit good processibility characteristics in an alloy. This problem may be aggravated with the inclusion in the composition of fillers that may improve desirable characteristics of the formed composites but also further increase melt viscosity of the composition.
In view of the above, a need currently exists for improved polyarylene sulfide/liquid crystal polymer alloys and compositions including the alloys. In addition, a facile, low cost method of forming a polyarylene sulfide/liquid crystal alloy would be of great benefit.